U.S. patent number 4,077,006 [Application Number 05/672,066] was granted by the patent office on 1978-02-28 for bidirectional unicable switching system.
Invention is credited to Victor Nicholson.
United States Patent |
4,077,006 |
Nicholson |
February 28, 1978 |
Bidirectional unicable switching system
Abstract
A two-way cable television broadcasting system wherein a single
coaxial cable is used to deliver TV and FM programs to many
subscribers with each subscriber having a specific allocated band
of frequencies for reception of any desired television or FM
program and where each subscriber can independently select the
program desired to be seen and/or heard which will be delivered to
the subscriber over an allocated band of frequencies. The
subscriber drops from said coaxial cable are so arranged that they
descend in frequency along the length of the feeder cable.
Automatic switching of any incoming program to any drop is achieved
by means of converting all incoming channels to a common I.F.
frequency at an amplifier or control station and then deconverting
said frequency to the desired outgoing band of frequencies.
Inventors: |
Nicholson; Victor (Chevy Chase,
MD) |
Family
ID: |
24229485 |
Appl.
No.: |
05/672,066 |
Filed: |
March 30, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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558425 |
Mar 14, 1975 |
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405846 |
Oct 12, 1973 |
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Current U.S.
Class: |
725/119;
348/E7.053; 348/E7.075; 725/127 |
Current CPC
Class: |
H04J
1/10 (20130101); H04N 7/104 (20130101); H04N
7/17354 (20130101) |
Current International
Class: |
H04J
1/10 (20060101); H04N 7/10 (20060101); H04J
1/00 (20060101); H04N 7/173 (20060101); H04B
001/06 () |
Field of
Search: |
;178/5.1,5.6,5.8R,5.8A,DIG.23,DIG.13 ;325/53-55,5,64,308,309
;179/2TV ;358/84,86,114 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IEEE Spectrum Application Report on "Two Way Applications for Cable
Television Systems in the '70s," by Jurgen, 11, 1971, (pp.
39-54)..
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Primary Examiner: Griffin; Robert L.
Assistant Examiner: Ng; Jin F.
Attorney, Agent or Firm: Wray; James C.
Parent Case Text
This application is a continuation-in-part of Ser. No. 558,425,
filed Mar. 14, 1975, now abandoned; which is a continuation of Ser.
No. 405,846, filed Oct. 12, 1973, now abandoned.
Claims
I claim:
1. In a cable distribution system having a head end, means at said
heat end for receiving multiple television channels, a coaxial
cable having multiple channel capacity connected to said head end,
a bridger amplifier connected to the coaxial cable for receiving
and amplifying signals in the multiple television channels, a
control station connected to the bridger amplifier, said control
station including a switching network and channel converters
connected to the bridger amplifier, a feeder cable having a
plurality of subscriber allocated channels, said feeder cable
connected to the switching network and channel converters, a
plurality of subscriber drops connected to the feeder cable, each
subscriber drop being connected to a single subscriber allocated
channel in the feeder cable, thereby allocating one channel in the
feeder cable to each subscriber drop, means at each subscriber drop
for sending a control signal to the control station on the
subscriber allocated channel allocated to that subscriber drop to
control the switching network at the control station.
2. In a system set forth in claim 1, wherein means are located at
the subscriber drop for sending a television signal to the control
station on the same subscriber allocated television channel
allocated to the subscriber drop and means at said control station
for sending the television signal to other subscribers.
3. In a system as set forth in claim 1, wherein the allocated
channel frequencies are allocated to subscriber drops in a
descending order depending on the distance of such subscriber drop
from the control station.
4. In a system as set forth in claim 1 wherein means for sending
the control signal from a subscriber drop to the control station
comprises means for sending the control signal on the lower end of
the subscriber drops' allocated frequency.
5. The cable distribution system of claim 1 wherein the control
station switching network and channel converters comprise a first
plurality of channel converters connected to bridger amplifier for
converting multiple channels from the coaxial cable to a common
I.F. band of frequencies, a switching network connected to the
first converters, and a second plurality of converters connected to
the switching network and to the feeder cable for converting the
common I.F. band of frequencies to the separate subscriber
allocated channel.
Description
This invention relates to a two-way coaxial sending and receiving
system wherein a single coaxial cable is used to send and receive
television signals with each subscriber drop being assigned its own
specific allocated band of frequencies.
It is well known in the art that cable television systems today
have the capabilities of delivering up to 35 different television
channels of programming plus the full spectrum of FM services to
all subscribers. Existing systems are "party line" type systems
whereby the same programming is delivered to all subscribers. These
cable systems also have the capability of returning television
signals to the headend.
There have been other types of systems proposed in the past whereby
each subscriber has separate downstream and upstream cables thereby
permitting him to remotely select any available program. The
subscriber could dial the desired program and at a local switching
center, the subscriber's cable would be interconnected to that
channel. This type of switching system presents the possibility of
a subscriber being able to request television programs from
libraries of video tapes providing educational programs, foreign
language lessons, cultural or sporting events. This system had one
inherent weakness: the requirement for a separate feeder cable to
every subscriber. This requires the use, in either aerial or
underground construction, of large bundles of cables. This type of
system -- in spite of its promise -- has not succeeded in this
country, because of excessive costs.
It is the general object of this invention to provide the above
noted services by using a system wherein a single coaxial cable is
used to deliver television programs to many subscribers, where each
subscriber has a specifically allocated television channel or band
of frequencies for reception of desired programs, where each
subscriber independently selects the program to be sent on the
subscriber's assigned channel, where all subscribers can receive FM
signals, and where a descending order of television frequencies is
delivered to subscribers on the feeder cable. The same feeder
coaxial cable that is used for reception of the signal is used to
transmit back to the amplifier or control station a signal from the
subscriber to select the desired program.
A still further general object of this invention is the use of this
same feeder coaxial cable to send back to the control station a
television signal on the assigned channel. This program can be used
for two-way television of broadcast quality between any two
subscribers or for a conference of subscribers.
This invention is similar in concept to the prior art "Wired
Broadcasting Systems" shown by Eric J. Gargine, U.S. Pat. No.
3,665,331 and Ralph Porton Gabriel, U.S. Pat. No. 3,801,735. A
major difference in this system from the above systems is that
rather than providing two separate feeder cables to each subscriber
(one downstream, the other upstream), up to 35 subscribers can
utilize the same feeder cable for receiving signals downstream and
sending them upstream. Each subscriber on a given feeder coaxial
cable is allocated a separate channel for reception and
transmission of programs plus the transmission of control signals.
These channels are allocated to individual subscribers on the basis
of distance along the feeder from the control station with the
closer subscribers being assigned a higher frequency spectrum.
The primary advantage of this system along with the other switching
type wired broadcasting systems is that each subscriber has the
capability of remotely selecting one of possibly hundreds of
available television or other programs at any time. The immediate
applications using existing single trunk cable systems is primarily
one-way, downstream where the subscribers choice is limited to 35
television channels and full spectrum of FM as this is the total
delivered to each control station and therefore the total available
for connection to the subscribers who requested them. Later there
can be additional origination of programming at the control station
(which could be located in a public school or library). To further
increase the subscriber's program choices the cable operator can
duplicate the trunk part of the system. Other possible
applications, where the trunk part of the system is two-way, are
for the subscriber's return signals to be sent to other parts of
the system upon being received at the control station.
It is still a further object of this invention to apply it to multi
or single dwellings. Since both the downstream and upstream
services use the same bandwidth for each subscriber and since this
bandwidth is wide enough for a television channel, it is possible
for one or any number of subscribers to simultaneously originate
television programming. This programming can be automatically
routed back to the control station onto an upstream trunk line to
the headend, and then downstream to another preselected
subscriber.
It is a still further object of the instant invention that it is
distinguished from present CATV systems in the following
manner:
CATV systems generally have up to two line extender amplifiers
cascaded in the feeders from each output of the bridger amplifier;
the proposed system eliminates these line extenders. The limiting
factor for distance of subscriber service from a feeder, in a CATV
system, is the attention of the coaxial cable at the top frequency
for which the system is designed. The instant invention extends
feeders more than twice as far without amplification as its
limiting factor is the attenuation of the coaxial cable at channel
2. This feature provides reduced system cost and elimination of
system distortions as introduced in the line extenders. The feeder
is a coaxial cable whose size (and therefore attenuation) is
determined by the distance to the furthest subscriber. Several
feeder cables can be paralleled for areas of high density of
homes.
The above mentioned and other features and objects of this
invention and the manner of attaining them will become more
apparent and the invention itself will best be understood by
reference to the following description of embodiments of the
invention taken in conjunction with the accompanying drawing the
description of which follows:
FIG. 1 is a diagrammatic representation of the Trunk, Bridger and
Control Station and feeder cable of the instant invention which is
similar to a conventional CATV system such as that shown in
"Two-way Applications for Cable Television Systems in the 70's."
(Ronald K. Jurgen, Spectrum of IEEE, November 1971, FIG. 4, page
45.) A significant difference however is the elimination of line
extender and the modifications to the Trunk and Bridger Station to
include a Control Station.
FIG. 2 is a diagrammatic representation of a typical feeder cable
showing the Control Station terminal and the coaxial cable
disclosing subscriber drops along its effective length.
FIG. 3 is a diagrammatic representation from the Control Station
showing the downstream paths of the television signals to the
individual subscribers.
FIG. 4 is a diagrammatic representation of the Control Station
showing the downstream, upstream and control signal paths.
FIG. 5 is a diagrammatic representation of a section of the Control
Station that processes the subscriber's control signal.
FIG. 6 is a diagrammatic representation of a two-way subscriber
drop from the feeder cable to the receiver and back.
In present CATV systems, at some trunk locations, some of the
broadband TV and FM signal is split off with a directional coupler,
amplified in a bridger amplifier and distributed down feeder lines
which pass the various subscriber locations. For those wishing to
subscribe, a tap is made into the feeder cable and to a cable drop
to the subscriber's residence, which drop is connected to the
subscriber's TV set. All channels are on the cable and are received
by all subscribers.
This system incorporates separating into individual channels the
combined signals at the control Station, converting them to common
I.F. frequencies and switching each one to the desired outgoing
R.F. channel and feeder cable to satisfy the request of a
subscriber. The switching circuitry can be of any type capable of
being controlled by a remote voltage. Therefore, by the application
of a frequency selective voltage, any subscriber can have any
channel connected to his/her feeder cable.
As by way of example the frequency allocation to each feeder can be
as follows:
______________________________________ SUBSCRIBER FREQUENCY
ALLOCATIONS Subscriber No. MHz
______________________________________ 1 294 - 300 2 288 - 294 3
282 - 288 4 276 - 282 5 270 - 276 6 264 - 270 7 258 - 264 8 252 -
258 9 246 - 252 10 240 - 246 11 234 - 240 12 228 - 234 13 222 - 228
14 216 - 222 15 210 - 216 16 204 - 210 17 198 - 204 18 192 - 198 19
186 - 192 20 180 - 186 21 174 - 180 22 168 - 174 23 162 - 168 24
156 - 162 25 150 - 156 26 144 - 150 27 138 - 144 28 132 - 138 29
126 - 132 30 120 - 126 31 82 - 88 32 76 - 82 33 70 - 76 34 64 - 70
35 58 - 64 ______________________________________ Note: 88 - 108
MHz is used for F. M. signals to all subscribers. 108 - 120 MHz is
not used as it includes aircraft navigation band - even though
there should be no radiation problem.
In the following detailed description and the drawing, like
reference characters indicate like parts.
In FIG. 1 is shown a Trunk and Bridger Amplifier and Control
Station where the Control Station 1 receives signals from the
bridger amplifier 2 and sends them to the subscribers. It also
receives signals from subscribers and sends them upstream to the
cable system headend by way of the Return Trunk Amplifier 3.
In FIG. 2 is shown a Control Station 1 and a feeder cable 10,
descending from said Control Station. The closest subscriber 4 is
allocated the TV channel spectrum of 294-300 MHz plus the FM
spectrum 88-108 MHz and the most distant subscriber 5 is allocated
the TV channel spectrum 54-60 MHz plus the FM spectrum of 88-108
MHz. The other subscribers on the feeder cable are assigned TV
channel spectrums in a descending order plus the FM spectrum 88-108
MHz.
In FIG. 3 is shown the downstream functions of the Control Station
1, to one of the feeder cables, which receives the multichannel
output of the bridger amplifier 2 through directional couplers 6
and processes each TV channel separately, through the down
converters 7 that provides a common I.F. band of frequencies 41 to
47 MHz. The outputs of these converters are connected with further
directional couplers 6 to the input terminals of switching network
8. The output of the switching network connects the requested
channel's I.F. to TV channel up-converter 9. This switching can be
mechanical, electronic or any automatic type where a desired
program can be sent to the proper channel converter through
additional directional couplers 6 to feeder cable 10. Local TV
program origination whether live or by tape is handled the same
way. This is shown by videotape player 11 connected to modulator 12
for conversion of video to I.F. and is available to be switched to
any subscriber. By this system the Control Station connects any
desired I.F. modulation to any output channel on any feeder.
The FM signals are handled differently in that the broadband
spectrum 88-108 MHz is maintained throughout; further directional
couplers 6 connect the bridger amplifier's output to FM amplifier
13 and the various feeder coaxial cables 10. By this system the
Control Station connects FM to all feeder cables.
In FIG. 4 is shown the downstream, upstream and control functions
of the Control Station 1. The downstream functions are the same as
shown in FIG. 3 with signals from bridger amplifier 2 being
connected via directional coupler 6, being converted to I.F. by
down-converter 7, being switched by 8 to the desired channel
up-converter 9 and connected to the feeder cable 10 through a
channel bandpass filter 14.
The upstream television signals from feeder cable 10 are fed
through directional coupler 6, through the channel bandpass filter
14, through other directional couplers to an I.F. down-converter 7,
then through the automatic switch network 8 to the desired channel
up-converter 9 and through a directional coupler to the return
trunk amplifier 3, in the Trunk and Bridger Amplifier and Control
Station. These functions enable the TV or data return channels to
be ultimately fed to the Cable System headend, there to be
redistributed to any other subscriber.
The upstream control signals are fed to the frequency selective
voltage control network 15 where they provide frequency selective
voltages to control the automatic switching of both upstream and
downstream signals. For a detailed description of this network see
FIG. 5.
In FIG. 5 is shown various functions that are employed in
controlling the switching network that allocates the television
channels being sent and received by a subscriber. This is done by a
network that receives and responds to a control signal from a
subscriber. A subscriber can send this signal by modulating with a
discrete frequency the lower R.F. band edge of the subscriber's
allocated channel. All taps, cable, filters and accessories on the
feeder cable 10 are two-way so this control signal is split off the
feeder at the Control Station by a directional coupler 6, connected
to channel R.F. bandpass filter 14, to an R.F. detector 16, then a
low frequency bandpass filter 17 that accepts the desired frequency
selective signal and feeds it to amplifiers and that develops a
control voltage for the automatic switching. Items 16, 17 and 18
are components of the frequency selective control network 15 in
FIG. 4. Items 6, directional couplers, which are in the control
path after 14 are not shown on this FIG. 6.
The conversion of any incoming television channel at the Control
Stations to an outgoing television channel is accomplished by
converting all incoming channels to a common I.F. frequency,
switching them by means of control signals and then reconverting
them to the desired outgoing frequency.
The switching, which is not shown, can be typical of any of those
that are employed in two-way cable television systems such as that
shown at the program exchange in U.S. Pat. No. 3,801,705 of
Gabriel, referred to above, for non-duplication or other services.
It can be electronic, mechanical or any automatic type wherein the
control signal from any subscriber will actuate the switching
circuit and cause the desired program to be sent to the
subscriber.
In FIG. 6 is shown a two-way subscriber drop which includes the
two-way feeder cable 10, directional coupler 28 and an FM bandpass
filter 19 to pass FM to the subscriber irrespective of TV channel
allocation. The feedthru section of the FM filter connects all TV
signals to a TV channel bandpass filter 14, to the subscriber's
two-way interface terminal 20 and to the TV receiver 21.
The upstream TV transmitting circuit can comprise of a TV camera
22, microphone 23 and modulator 24. An upstream control signal
transmitting circuit could include a lower band edge R.F.
oscillator 25, a discrete low frequency oscillator 26 and a mixer
or modulator 27. This control signal can be switched on by the
subscriber's interface terminal 20.
While the principles of the invention have been described in
connection with specific apparatus, it is to be clearly understood
that this description is made only by way of example and not as a
limitation to the scope of the invention.
* * * * *